1. Field of the Invention
The present invention relates generally to lasers and more particularly to an improved ceramic structure for use as the pumping cavity in flash lamp pumped, solid state lasers.
2. Description of Related Art
When certain high gain laser materials such as neodymium-doped yttrium aluminum garnet (Nd:YAG) or neodymium-doped gadolinium scandium gallium garnet (Nd:GSGG) are pumped to a condition of large population inversion, for example in order to achieve Q-switching, a saturation effect occurs which limits the laser output energy obtainable regardless of the level of input pumping energy. This saturation is caused in part by a laser depumping phenomenon resulting from the fact that a significant amount of fluorescent radiation at the lasing wavelength escapes laterally from the laser rod into the surrounding pumping cavity and is reflected by the pumping cavity back into the laser rod. This return radiation stimulates decay from the upper laser transition level, thereby effectively limiting the number of excited ions which can occupy that level and, in turn, limiting the maximum output energy obtainable from the laser.
In order to overcome the above problems, solid state lasers are typically constructed so that both the laser rod and the pumping flash lamp are housing within a samarium-doped glass tube. The samarium-doped glass provides absorption of radiation at the lasing wavelength (1.06 microns) while providing transmission of the pumping radiation.
The samarium-doped glass tube is surrounded with a material having a high diffuse reflectivity to achieve uniform illumination of the surface of the laser rod by the pumping radiation. The material typically used to provide the desired high diffuse reflectivity is barium sulfate. When barium sulfate powder is used, it is usually tightly packed between the samarium-doped tube and an outer concentric aluminum tube. Alternatively, the barium sulfate powder is mixed with conventional plasticizers and binders and sintered to form a ceramic body used to surround the doped samarium glass tube. These ceramic bodies are generally referred to as pump cavity bodies or simply pump cavities.
U.S. Pat. No. 3,979,696 discloses a Nd:YAG pump cavity in which a fused quartz or borosilicate glass tube is coated with a polycrystalline powder, such as samarium oxide. The samarium oxide coated tube provides the same desirable adsorption as the samarium-doped glass tube, and is much less expensive. The contents of this patent are hereby incorporated by reference.
Although the above-described pump cavities have been found to be suitable for their intended purpose, there has been a continuing need to develop new materials having high diffuse reflectivity to replace the conventionally used barium sulfate. Although barium sulfate provides excellent diffuse reflectivity, it is an inherently weak material which has a flexural strength of only 600 pounds per square inch (40.83 atmospheres). Pump cavity bodies which utilize barium sulfate also tend to be expensive to make, are dusty thereby contaminating the optics and are easily broken or cracked.
Accordingly, there is presently a need to provide new materials to replace barium sulfate as the diffuse reflector material, particularly in Nd:YAG laser pump cavities. The new material should provide a high level of diffuse reflection which is comparable to barium sulfate while at the same time being easily molded or otherwise shaped and sintered to form a strong pump cavity body which is dust free and is resistant to breakage and fracture.